The objective of this study is to investigate the validity of the Sensory-Decision-Theory Approach to the measurement of two components - sensory discriminability and reporting bias - in the response of experimental pain. The mathematical relationship of the indices of sensory discriminability and reporting bias has been studied. The results of the investigation indicate that when sensory discriminability changes, the estimation of reporting bias by SDT approach is no longer appropriate. A Monte-Carlo study has been designed and will be carried out to examine the sampling behavior of these two indices under various statistical assumptions. A report of this study will soon be prepared.